skills: add writing-implementation-plans, receiving-code-review, finishing-development-branches

Evaluated obra/superpowers and JuliusBrussee/caveman for gaps in the
existing library. These three fill real ones (plan-to-delegate handoff,
evidence-based review triage, completion vs. integration authority);
adapted for this fleet's Gitea/RLS/multi-delegate conventions. Everything
else in both repos duplicated existing skills or didn't fit (see README
Provenance note on caveman).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -92,6 +92,14 @@ than assuming the delegate can fetch it itself.
   rebase conflict by tracing each side's intent; never `--abort`.
 - `tdd` -- red-green-refactor test-driven development, one vertical slice
   at a time, at pre-agreed seams.
+- `writing-implementation-plans` -- turn settled requirements into
+  self-contained, dependency-aware tasks that memoryless delegates can
+  execute and verify without the originating conversation.
+- `receiving-code-review` -- verify incoming review findings against the
+  actual codebase and spec before accepting, rejecting, or implementing them.
+- `finishing-development-branches` -- verify the exact branch tip, confirm
+  its base, and require an explicit integration choice before merge, Gitea
+  push/PR, or cleanup.
 
 ## Provenance
 
@@ -105,6 +113,8 @@ each skill's frontmatter:
 - [Mte90/linus-torvalds-skill](https://github.com/Mte90/linus-torvalds-skill) (CC0-1.0)
 - [mattpocock/skills](https://github.com/mattpocock/skills) (MIT)
 - [Leonxlnx/taste-skill](https://github.com/Leonxlnx/taste-skill) (MIT)
+- [JuliusBrussee/caveman](https://github.com/JuliusBrussee/caveman) (MIT;
+  evaluated, no skill retained)
 
 ## Vetting external skills
 
@@ -125,4 +135,4 @@ When a real, non-obvious pattern or gotcha comes up more than once,
 write it down here rather than re-discovering it next time. Keep each
 skill focused on one concern, include the *why* (not just the *what*) so
 future edge cases can be judged sensibly, and prefer concrete confirmed
-incidents over generic advice.
+incidents over generic advice.